Although he’d settled on using ATTiny85’s for this project, [Tyson] was fresh out of through-hole versions. He decided to skip the prototyping phase and go right for fabrication, cranking up the laser-jet printer for some toner-transfer, which successfully produced 4 functioning boards (and 3 failures). The fireflies were [Tyson’s] first attempt at SMD soldering, and we’d have to say it’s a job well done; he reflowed each board with a cheap-o heatgun from Harbor Freight.

After some hiccups with fuse programming, [Tyson] got the code uploaded and the fireflies illuminated. Swing by his site for the nuts and bolts on construction, then snag the project files here. (Direct .zip download)

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10 thoughts on “Low-Power SMD Fireflies”

Good newbie project. I haven’t done any SMD soldering yet either, but I think it would have helped to prevent solder bridging by putting flux on the board before adding solder pads. I’m surprised he has 30+ days of LED illumination on a 3v CR2032 powering the ATTiny85 — I’ve recently had problems with 9v batteries on a 5v regulator lasting less than a week with a similar setup, but I’ve also been using multiple LEDs that also seem to draw more mA per hour than this project…so I’m now using a bridge rectifier >> softener cap >> volt. regulator >> more caps >> ATTiny85 setup using the 15v AC line that powers my old doorbell as a more permanent power source.

I built a tiny85-based firefly jar with six charlieplexed LEDs that’s been running since last May on a CR2450 (slightly bigger battery, but still…). It flashes a sequence of LEDs every few minutes. It also has a mercury switch, in it so you can shake the jar and make them ‘angry’. They flash more often for a while when you do that.

I was also pretty surprised to get so much life out of them. Although, the LED is on very little time, it only blinks every once in a while, and when it does it pulses with about ~9% duty cycle. From the datasheet, I imagine the idle current draw is somewhere between 50 and 100 uA, so it shouldn’t use too much power.

Last I checked, they’re still running strong on the original batteries. How long they’ll actually last, I have no idea.

As for the 9v to 5v regulator. I’d suspect you may have been dissipating a lot of power in the regulator itself. A typical 7805 might use a constant 5 mA or more even when idle.

A 7805 will still have a quiescent current in the mA range, and may not provide much benefit over the LM317.

You might look at different regulators to get a better quiescent current. Like the MCP1702, uses 2 uA quiescent current (less than 0.1% of the 7805 current), but it won’t source as much current as the 7805, maybe ~250 mA. If you need more current for other components, you might place them in line with a transistor and current limit them from the 9v.

Full disclosure: I’ve never used an MCP1702, but it looks like a good candidate for lower power devices.